Among the first was Japan's NTT DoCoMo, which showed off a prototype modular smartphone at an exhibition in Japan in 2009. Users could attach modules to it to customize the phone to their needs. Ideas at the time included a blood tester, a rollable e-paper screen and an electronic flute.

The device never went on sale and appeared a good deal clunkier than Project Ara, which will allow users to snap components such as a processor, camera and extra memory into a fixed frame.

Israeli handset maker Modu had a similar idea around the same time, producing a concept phone that had a minimum of features but could be snapped into a larger case that performed other functions.

One version of the original Modu has made it to market in Tel Aviv. The case can serve three functions: a camera, a speaker or an exercise band.

More recently, in 2011, Microsoft applied for a patent for a smartphone in which components could be swapped in and out. Microsoft envisaged them including a keyboard, a gaming pad, a second battery pack or an additional screen.

Microsoft also proposed a different phone that would come in two parts: one holding the main display and a second, smaller unit with the microphone and earpiece. The idea was that the user could continue to use the touchscreen and apps while holding the other part to their ear.

More details on Ara are expected Tuesday, when Google begins a two-day developer event to stoke interest in an idea that was launched by Motorola engineers when that company was part of Google. Google is webcasting the event.